Brazing jig for finned heat exchanger envelopes



Ot- 21, 1952 D. G. PETERSON BRAZING JIG FOR F INNED HEAT EXCHNGER ENVELOPES Filed May 21, 1951 W o L@ f 0Rl au s 3 3 2S S VO O K S7 E ST C EE EE 0 BE BE l. SH SH As 4AS 81M.

IN VEN TOR. `@mf/c7 Eek/Son BY im TTORVEY Patented Oct. 21, 1952 BRAZING JIG FOR FINNED HEAT EX- CHANGER ENVELOPES f David G. Peterson, Wellsville, N. Y., assgnor to The Preheater Corporation, New York,

' Applicationv May 21, 1951, Serial No. 227,420

The present invention relates to improvements in plate type exchangers utilized for` the trans-l mission of heat between two confined fluids and particularly to an improved method of assembling heat exchanger envelopes having walls provided with fins as extended surface.

A well known type of apparatus for the transfer of heat between two conned fluids is made up cfa plurality of metallic plates spaced to form passages through alternate ones of which a relatively hot iiuid, such as a hot gas, flows while air or other fluid to be heated traverses the intermediate passages.` In many such exchangers a series of envelopes are provided consisting of parallel plates with the space therebetween closed along one pair of opposite edgesvto bound opposite sides of the passage for the heating fluid. The envelopes are mounted in spaced parallel relation to form the passages for the fluid to be heated and the inter-envelope spaces are likewise closed along one pair of 'opposite side edges of the envelopes, which sides may be those extending parallel to the closed sides of the gas envelopes in case of parallel flow, or along the adjacent sides in case of transverseflow. Such spaced envelopes form a core that is usually `er1- closed within a housing with which are associated the inlet and outlet manifolds and the supply and discharge ducts for the two iiuids.

To increase heat transfer efflciency the walls of the fluid passages are frequently provided with :tins projecting into the path of the fluids and serving to increase the conduction'of heat to and through the walls that boundthe-.passages In the application of Sven Holm et al., Serial No. 752,008, dated June 3, 194'7,v there is disclosed forms of extended surface for passage walls comprising wires sinuously bent to form U-shaped loops whose legs constitute pin-like fins projecting from the walls bounding the passage within the envelope. On the outer face of these walls extended surface is provided in the form of channel members extending parallel to the direction of fluid flow. To promote sufcientheat transfer good bonds have to be provided between the pin iin elements on the inner walls of the gas ypassage and also between the outer walls of this passage and the channel members and such bonds have heretofore been provided bybrazing as disclosed vin Hodson and Holm application Serial No. 152,952, filed March 30, 1950.

`The present invention is directed toA an improved method and means for assembling vthe plates that form the passage walls and the sinuously looped elements and *channelsl that constil6 Claims. (Cl. 113-99) 2 v v tute extended surface from these walls so as'to form an integral heat exchange envelope. In carrying out the invention the parts of the finned envelopes are assembled in their final relative positions and held so positioned in a novel assembled jig that also serves as part of a wrapping of a shroud that shields the envelope so as lto assure uniform distribution of brazing heat to the parts of the envelope and protect it from the deleterious effects that might result from nonuniform heating.

The invention will best be understood upon consideration of the following detailed description .of illustrative embodiments thereof when read in conjunction with the accompanying drawings in which:

f Figure l is an exploded perspective view of an envelope assembling and shroud embodying the invention. v

Figures 2 and 3 are broken away transverse and longitudinal section views, respectively, through an assembled brazing shroud containing a heat exchange envelope in preparation by the brazing.

As mentioned above heat exchangers of the type contemplated herein are made up of a 'plurality of unitary envelopes comprising metal plates II and I2 mounted in spaced relation to form a gas passage designated I3 in Figure 3 while the spaces outside thewalls II and I2 and located between adjacent envelope components of aV complete heat exchanger form the air passages or vice versa. 'Io provide extensive surface in the gas passage I3 a plurality of iin elements are mounted between the inner surfaces of the walls II and I2 these'comprising wires sinuously bent to form U-shaped loops extending back and forth between the passage walls and whose legs constitute pin-like iins I 4. To facilitate bonding these sinuous elements t-o ythe passage walls II, I2, channel members I6 are fitted over and along the bight portions 'of the sinuously bent elements Illl as described in greater detail in the aforesaid Hodson and Holm application Serial No. 152,952, filed March 30, 1950. Opposite the looped elements I4 in the gas passage I3 channel members .I1 are mounted to extend longitudinally of the` outer surface of the walls I I, I2 -to constitute extended surface therefrom that will be located inithe air passages when a series of envelopes are assembled in superposed relation to constitute a heat exchanger core in usual fashion. Tohold the passage Wall plates II, I2 and the finned elements therebetween and the channel members on the outer faces of the walls in assembled relation for brazachter? ing, a number of tack welds may be formed at longitudinally spaced points between channels I6 and the inner faces of the walls II, I2 and between the channels I 'I and the outer faces of Walls I I, I2. Strips or sheets of brazing metal were previously disposed on the plate surface and Within the ychannel I6 as these parts are assembled. 'I'he heat exchanger envelope with extended surface on both the inner and outer walls of the passages II, I2 is then in preliminary assembled relati-on and ready for brazing to finally bond the iins to the Walls. An individual heat exchanger envelope component I9 so prepared is indicated more or less diagrammatically .in Figure l.

The first step in the brazing operation is to position a plurality of bars in side `by side relation parallel to cach other as on the rolls 2I of ay conveyor leading to the brazing oven. The number of bars 20 utilized is determined by the Width of the envelope I3 so that the transverse row is Wide enough torslightly overlap the sides of the envelope. Each of the bars 20 is provided with several transverse grooves 22, as adjacent its ends, and with these notches in adjacent bars alined they may -be locked together by insertion of llocking strips 23. The locking strips 23 havea'further function in orienting the envelope I9 within vthe jig, being provided with a row -of pins 24 positioned in spaced relation corresponding to the spacing of the channel members VI'I tacked to the outer faces of the `envelope walls II, I2. The bars 26 having been looked together by the strips 24 a sheet 23 of asbestos or other insulating material is mounted over the bars 20 and pressed down yso that the pins 24on the locking strips 23 Yprojectabove the surface of vthe asbestos sheet 25. The `loosely assembled envelope I9 is then placed in position so that the pins 24 .on` the Vlocking strips 23 enter thegrooves of the channel, n elements II near the ends thereof .or-at other-.locations also. The operation continues by mounting a second asbestos sheet, other locking Astrips 23 Vand bars 20 on the top side of the envelope I9. The longitudinal side edges of the asbestos sheets are then lfolded toward each other as indicated in Figure 2 and suitably held together, as by ad-i hesive tape 23. Finally-a rectangular frame 28 is lowered over the jig. andenvelope to enclose the assembly along the sides and ends thereof.

The employment of a shroud enclosing the heat exchange envelope I9 minimizes distortion of the latter during brazing. This is because the shroud acts as a radiation shield to Vreduce the over-all rate of heating so that the various components of the envelope heat more uniformly. The shroud also eliminates heating the metal chiefly along thc edges of the envelope because when enclosed the envelope IKS with its various .parts is heated from top to bottom uniformly throughout its cross section. When utilizing a shroud, it has been -found preferable in Vorder to minimize distortion to rspot weld the iin channels I6, I1 only oncealong each length, as near their midpoints, so as to permit the channels and plate to expand at rdifferent rates without producing distortion. To permit this it is necessary to maintain the channels properly oriented during the brazing operation and this is accomplished by the pins 24 on the locking and positioning strips 23 which hold the channels in proper transversely spaced relation Within the shroud. The asbestos sheets 25 between the envelope I9 and parts ofthe jig including theframe 28 give conf 4 tinuity tothe shroud and act as a radiation shield at those points where gaps might exist between the sides of adjacent parallel shroud bars 20.

This type of brazing employs the use of a protective atmosphere. The use of a shroud previously described hinders the free passage of the atmosphere to the work. Therefore we have adopted a method of purging the envelope interior of the entrapped air (oxygen). Alcohol or vsimilar fluid is used as a purging medium and a small quantity is placed in the interior of the envelope. As the work passes into the furnace, through the flame curtain the alcohol ignites, purging Vthe envelope of the entrappcd oxygen.

What I claim is:

1. A brazing assembly jig for a heat exchanger envelope that includes spaced, rectangular walli'orming metallic plates provided on their outer surfaces vwith longitudinally extending metallic ns, said jig comprising; a row of similar shroud bars disposed in abutment in side by sideY relation and each having transverse Yslots .at.v longl? tudinally spaced points alined with correspondingly located slots in adjacent .bars to .form .transverse locking grooves; locking'strips seated in said grooves and maintaining the transverse alinement of said shroud bars; a 'row of. positioning pins on .each locking bar spaced :apart to conform. to thev spacing ,of the channels 4on the envelope andv adapted .to engage :the ,longitudinal nns `ensaid heat exchangerenvelope; .a second set of .locking strips v.and slotted shroud bars superimposed on aheat .exchanger .envelope-supported-.on said Vshroud bars; and a rectangular frame member .surrounding andrenclosing the .asseniblyv` of .heatexchanger .envelope sandwiched between vupper ,and lower .layers .of shroud bars.

Z. A brazing jigassembly foraheat .exchanger envelope that includes spaced, rectangularrwallforming metallic plates .provided on their ,outer surfaces withlongitudinally..extending ns in the form of transverselyspaced....metallic channels, said jig comprising; a rowof similarshroudjbars disposed in vabutment inside byside relationand each havingtransverse slots at .longitudinally spaced points alined withcoirespondingly located slots in adjacentbars -to form transverselocking grooves; locking strips Aseated in Vsaid .grooves and maintaining ,theltransverse.alinement of said shroud bars; arovv of positioning pinson cach locking barpspaced apart to conform to the Yspacing of A.the channels on the-envelope and adapted toengage' between the legs ,of the channelson said heat exchanger envelope; anasbestos sheet impaled. on the pins of said locking lstrips 'and folded over the side and end marginal edges of a heat exchanger envelope when positioned above said sheet and supported on said bars; a second asbestos sheet and other locking strips and slotted shroud bars superimposed on a heat exchanger envelope supported as aforesaid;;and a rectangular frame member surrounding Yand enclosing the assembly of heat exchanger envelope sandwiched between upper and lower layers of shroud bars.

3; A brazing 'jig' assembly lfor a heat exchanger envelope that 4includes spaced, rectanfV gular wall-forming metallic plates provicledon their outer surfaces with ltransversely spaced longitudinally extending metallic nns. said jig assembly comprising; -a row 'of similarLshroud bars disposed inl abutment in side by side rela# tion and each having transverse slotsat ',longi' tudinally spaced points Aalincdlwith correspondingly` `located .slots of adjacent bars-toform transverse.V locking grooves; locking strips seated in said locking grooves and maintaining the transverse alinement of said shroud bars; a row of positioning pins on said locking bars spaced apart to conform to the spacing of the channels on the envelope and adapted to engage the ns on said heat exchanger envelope; an asbestos sheet impaled on the pins of said locking strips and projecting folded over the side and end edges of a heat exchanger envelope when positioned above said sheets and supported on said bars; a second asbestos sheet and other locking strips and slotted shroud bars superimposed on a heat exchanger envelope supported as aforesaid; and a. rectangular frame member surrounding and enclosing the assembly of heat exchanger envelope sandwiched between upper and lower layers of shroud bars.

4. A brazing jig assembly for a heat exchanger envelope that includes spaced, rectangular wallforming metallic plates provided on their outer surfaces with transversely spaced longitudinally extending metallic ns, said jig assembly comprising; a row of similar shroud bars disposed in abutment in side by side relation and each having transverse slots at longitudinally spaced points alined with correspondingly located slots of adjacent bars to form transverse locking grooves; locking strips seated in said locking grooves and maintaining the transverse alinement of said shroud bars; a row of positioning pins on said locking bars spaced apart to conform to the spacing of the channels on the envelope and adapted to engage the i'lns on said heat exchanger envelope; an asbestos sheet impaled on the pins of said locking strips and projecting folded over the side and end edges of a heat exchanger envelope when positioned above said sheets and supported on said bars; a second asbestos sheet and other locking strips and slotted shroud bars superimposed on a heat exchanger envelope supported as aforesaid; and a rectangular iramemember surrounding and enclosing the assembly of heat exchanger envelope sandwiched between upper and lower layers of n shroud bars, fthe marginal edges of the upper and lower Aasbestos sheet being joined to fully enclose the heat exchanger positioned therebetween.

5. A brazing jig assembly for a heat exchanger envelope that includes spaced rectangular wallforming plates provided at their outer surfaces with longitudinally extending fins, said jig comprising; a row of shroud bars disposed in side by side relation and each having a transverse slot alined with the correspondingly located slot in adjacent bars so as to forma transverse locking groove; a locking bar seated in said groove and maintaining the transverse alignment of said shroud bars; means on said locking bar adapted to conform to the spacing of the fins on said plates; a second set of slotted shroud bars having a locking strip tted therein and superimposed on an intervening heat exchanger envelope supported on said lower shroud bars; and a frame member surrounding said heat exchanger envelope sandwiched between upper and lower layers of shroud bars.

6. A brazing jig assembly for a heat exchanger envelope that includes spaced rectangular wall-forming plates provided at their outer surfaces with longitudinally extending fins, said jig comprising; a series of abutting shroud bars each having a transverse slot alined With the corresponding slot in adjacent bars so as to form a transverse groove; locking means in said groove for maintaining the transverse alignment of the shroud bars, said means comprising a row of positioning pins spaced so as to conform to the spacing of the iins on said envelope; an asbestos sheet impaled on said positioning pins and projecting over the side and end edges of the heat exchanger envelope when positioned above said sheet and supported on said shroud bars; a second asbestos sheet and slotted shroud bars having a cooperating locking means superimposed on the heat exchanger envelope; and a frame member surrounding the assemblsr of heat exchanger envelope sandwiched between upper and lower layers of shroud bars.

DAVID G. PETERSON.

REFERENCES CITED The following references are of record in the iiie of this patent:

UNITED STATES PATENTS Number Name Date 1,836,619 Ritter Dec. 15, 1931 2,310,841 Curtis Feb. 9, 1943 

